The description that follows refers mainly to implanted medical devices such as pacemakers, cardiovertors or defibrillators, but it should be understood that the invention also can be implemented with simple Holter devices, including external devices, for the monitoring and the ambulatory recording of a patient's cardiac activity.
The typical architecture of the electronic circuits of a pacemaker or implantable cardiac defibrillator includes a central processing unit, with a memory of the ROM type (read-only memory) integrated into a microcontroller and containing the software operating code (instructions) making it possible to control the cardiac prosthesis, as well as a memory of the RAM type (read-write random access memory) of larger capacity for the storage of medical data collected (i.e., detected or sensed) by the prosthesis. The circuit architecture also comprises elements suitable for interfacing with the analog circuits (e.g., preamplifiers, filters, signal conditioning circuits, input output interfaces and protection circuits), and eventually a DMA (direct memory access) circuit and different peripheral components necessary to the functioning of the prosthesis.
A first difficulty with this type of classical circuit architecture lies in the difficulty to update the software operating code. Indeed, to update this code an operation known as “remasking” the microcontroller (or microprocessor) is necessary. This operation is done by the manufacturer of the circuit (i.e., at the foundry) and requires a long time, typically from two to three months, to complete. When the new circuit is delivered, it then needs to be incorporated into the prostheses manufacture, which may require two to three additional months to achieve, corresponding to the complete duration of a conventional industrial production cycle. Thus, the time between the development of a new version of the software code and its commercial introduction into products deliverable to the physician is in general of at least six months.